Luminescence display tube base plate comprising protrusions extended sideways beyond grid supports

ABSTRACT

In a base plate assembly including an insulative substrate for a luminescence display tube and grid supports formed on the substrate along side edges thereof, a plurality of protrusions are extended sideways from the body of the substrate beyond the grid supports. When each of the grid supports has a protrusion left after cutting of the supports from two frames, the protrusions of the substrate are extended beyond the protrusions of the grid supports.

United States Patent [191 Kobayakawa et a1.

[ Sept. 17, 1974 LUMINESCENCE DISPLAY TUBE BASE PLATE COMPRISING PROTRUSIONS EXTENDED SIDEWAYS BEYOND GRID SUPPORTS Inventors: Masaki Kobayakawa; Kazufumi Yawata; Shigeru Yamashita, all of Kagoshima, Japan Assignee: Nippon Electric Kagoshima,

Limited, Kagoshima, Japan Filed: Sept. 17, 1973 Appl. No.: 397,796

Foreign Application Priority Data Sept. 20, 1972 Japan 47-110000 Nov. 7, 1972 Japan 47-128749 US. Cl. 313/108 R, 313/1095 Int. Cl....- H0lj I/92, HOlj l/94 Field of Search 313/108 R, 109.5

[56] References Cited v UNITED STATES PATENTS 3,705,324 12/1972 Masuda 313/108 R 3,800,178 3/1974 Farina 313/108 R Primary Examiner-James W. Lawrence Assistant Examiner-Wm. H. Punter Attorney, Agent, or Firm.lohn M. Calimafde [57] ABSTRACT In a base plate assembly including an insulative substrate for a luminescence display tube and grid supports formed on the substrate along side edges thereof, a plurality of protrusions are extended sideways from the body of the substrate beyond the grid supports. When each of the grid supports has a protrusion left after cutting of the supports from two frames, the protrusions of the substrate are extended beyond the protrusions of the grid supports.

4 Claims, 4 Drawing Figures BACKGROUND OF THE INVENTION This invention relates to a base plate assembly used in a luminescence display tube for one or more of the numerals, symbols, and letters.

A display tube of the type described is known, wherein thermal electrons emitted from a cathode is directed through a grid to those of a plurality of luminescent segments arranged on the front or viewing surface of an insulative substrate which are selectively supplied with a positive potential to make the segment luminesce in a desired pattern. The grid serves to substantially uniformly distribute the electrons on the segments supplied with the positive potential. Usually, the grid serves also to accelerate the electrons. A display tube for substantially simultaneously displaying a plurality of desired numerals, symbols, and/or letters, herein called a plurality of digits, often comprises a plurality of grids, one for each digit. In addition, a luminescence display tube comprises an electroconductive film formed on the inside surface of a vacuum envelope enclosing the cathode, the grids, and the insulative substrate for the primary purpose of electrostatically shielding the inside of the vacuum envelope. In the following, this invention will be described in specific connection with a luminescence display tube for eight digits although the invention is equally well applicable to a luminescence display tube for a different number of digits, including one.

In a luminescence display tube, the insulative substrate and the luminescent segments formed on the substrate in a plurality of groups corresponding to the respective digits form a base plate assembly together with supports attached thereon for the cathode and the grids and leads extended outwardly therefrom for the segments, the cathode, and the grids. As will later be described in detail, it is quite astonishing that even an improved base plate assembly of'the conventional structure has still had various defects, such as relatively low efficiency of manufacture, production of spurious luminescence and/or display, and possible damage to the electroconductive film.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a base plate assembly of a luminescence display tube, manufacturable with high efficiency.

It is another object of this invention to provide a base plate assembly of a luminescence display tube, which will not damage the electroconductive film formed on the inside surface of the vacuum envelope.

It is still another object of this invention to provide a base plate assembly of a luminescence display tube, capable of preventing the display tube from producing spurious luminescence and/or unwanted display.

In the manner known in the art, a base plate assembly of a luminescence display tube includes an insulative substrate, the display tube comprising a cathode disposed in front of the substrate and means, such as a grid or plurality of grids, for controlling distribution of electrons emitted by the cathode on the front surface of the substrate. The assembly further includes supports for the electron distribution controlling means formed thereon along side edges thereof. According to this invention, protrusions are extended sideways from the side edges of the substrate beyond the supports for the electron distribution controlling means.

Each of the supports for the electron distribution controlling means may have a protrusion left after cutting thereof from a frame. The protrusions of the substrate are extended beyond the protrusions of the supports for the electron distribution controlling means.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 is a schematic perspective view, partly cut away, of a luminescence display tube;

FIG. 2 is a schematic perspective view of an improved base plate assembly of the conventional structure;

FIG. 3 is a similar view of a base plate assembly according to a first embodiment of the instant invention; and

FIG. 4 is a like view of a base plate assembly according to a second embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Before describing a few preferred embodiments of the present invention, the background of the invention will be detailed with reference to FIGS. 1 and 2 in order to facilitate understanding of the invention.

Referring to FIG. 1, a luminescence display tube for a plurality of digits comprises a vacuum envelope 11, a base plate assembly 12 held within the envelope 11 by means not shown, a cathode 13 extended within the envelope ll longitudinally thereof in front of the base plate assembly 12, a plurality of grids 14 interposed between thecathode I3 and the base plate assembly 12, one for each digit, and a plurality of stem leads 15 for the cathode 13, the grids l4, and anode segments of the base plate assembly 12. The grids 14 serve to distribute the electrons emitted by the cathode 13 substantially uniformly on the anode segments selectively supplied with a positive potential through the pertinent ones of the stem leads 15. On the inside surface of the vacuum envelope 11, an electroconductive film (not shown) is formed for the primary purpose of electrostatically shielding the inside of the vacuum envelope 11 from the electrostatic field which might disturb the behavior of the electrons within the vacuum envelope 11.

Referring to FIG 2, an example of the conventional base plate assemblies 12 comprises an insulative sbustrate 20 of a ceramic material, glass, steatite, or the like and a plurality of luminescent segments 21 arranged on the front surface of the substrate 20 in groups. It should be understood that the front surface of the luminescent segments 21 are preferably flush with the front surface of the substrate 20 and that such arrangement is also meant by the expression arranged on the front surface." The luminescent segments 23 of each group are arranged in.-a substantial figure of eight and comprises an additional segment for a decimal point and a further additional segment, which may be dispensed with, for a display of4. In the manner known in the art, each of the luminescent segments 21 forms an anode segment mentioned with reference to FIG. I together with an electroconductive layer (not shown) placed behind the luminescent segment. The base plate assembly 12 further comprises a plurality of segment leads 22a, 22b, 22c, 22d, 22e, 22f, 22g, 22h, and 22i connected to the electronconductive layers situated behind the corresponding luminescent segments 21, grid supports 23 for the respective grids 14 arranged on the front surface of the substrate in pairs along both side edges of the substrate 20, grid leads 241, 242, 243, 244, 245, 246, 247, and 248 connected to at least one each of the respective pairs of the grid supports 23, a pair of cathode supports 251 and 252, and a pair of cathode leads 261 and 262 connected to the respective cathode supports and 252.

The supports 24 and 25 (251 and 252) and the leads 22 (22a, 22b, and 221'), 24 (241, 242, 248), and 26 (261 and 262) are usually soldered to metallized layers (not shown), respectively, preliminarily formed on the front surface of the substrate 20. The connections between the electronconductive layers and the respective segment leads 22, between the grid supports 23 and the respective grid leads 24, and between the cathode supports 25 and the respective cathode leads 26 are formed through the printed circuit techniques preferably in layers interposed between layers of a laminated ceramic substrate 20. It is usual that the luminescent layers are subsequently laid on the respective electroconductive layers to form the luminescent segments 21. It has, however, been often the case that the luminescent layers are inevitably laid also on the supports 24 and 25 and on the leads 22, 24, and 26. The luminescent layers which happen to be laid on some or all of the grid supports 23 and on the grid leads 24 produce spurious luminescence thereat in operation. The luminescent layers which happen to be laid on some or all of the leads 22, 24,and 26 often bridge such leads. Inasmuch as a luminescent material is a semiconductor, each of such luminescent layers serves as a resistor of the order of from several hundred ohms to several kilohms to provide shorts between such leads 22, 24, and/or 26 and to provide unwanted display and superfluous loads to a power supply (not shown) for the display tube. Removal ofthe unwanted luminescent layers are quite troublesome.

Referring further to FIG. 2, the free ends of the leads 22, 24, and 26 may be connected together by frame members 271, 272, 273, and 274 into four groups. This enables the electroconductive layers to be formed electrically and simultaneously by applying a voltage therefor between the lead groups. The luminescent segments 21 may similarly be formed electrically and simultaneously. It has, however, been inevitable because each ofthe lead frames, such as those united together by the fram members 271, 272, and 273, comprises both segment and grid leads 22 and 24, that spurious luminescent layers are also formed where unwanted, such as on the grid supports 23. Although useful in raising the efficiency of soldering the leads 22, 24, and 26 to the substrate 20 and forming the electroconductive layers and the luminescent segments 21 on the substrate 20, adoption of the frame lead techniques is still defective in view of the relatively low efficiency of manufacture of the base plate assembly 12 and of the display tubes and production of the spurious luminescence. In addition, the frame lead techniques are not applicable to the grid supports 23 and the cathode supports 25. Soldering of the supports 23 and 25 one after another to the substrate 20 deteriorates the efficiency of manufacture not only because of the number of times of the soldering processes but also because of the difficulty in the precise positioning of such supports 23 and 25.

Referring now to FIG. 3, a base plate assembly 12 according to a first embodiment of this invention comprise similar components designated with like reference numerals as in FIG. 2. Unlike the conventional base plate assemblies exemplified in FIG. 2, the segment leads 22 are extended outwardly of the substrate 20 from the longitudinal ends of its front surface and the grid leads 24 are extended outwardly of the substrate 20 from the longitudinal ends of its back surface. It is thus possible to unit the segment leads 22 and the grid leads 24 into different groups by frame members 271 and 272 on the one hand and by frame members 273 and 274 on the other hand to obviate the unwanted display during operation and the consumption of superfluous electric energy. The grouping of the segment leads 22 and the grid leads 24 into different groups further enables the voltage for electrically forming the luminescent segments 21 to be supplied only to the seg ment lead groups united together by the frame members 271 and 272. This avoids the unwanted formation ofthe luminescent layers on the grid supports 23 to sufficiently raise the efficiency of manufacture and prevent the spurious luminescence from being produced during operation. The grid leads 24 are shown in FIG. 3 extended farther than the segment leads 22 for mere convenience of illustration. Inasmuch as the electrons emitted by the cathode 13 do not acquire sufficient energy on reaching the cathode supports 251 and 252 supplied with the substantially same potential as the cathode 13, the spurios luminescent layers, if formed on thesesupports 251 and 252, do not luminesce. It is therefore possible to group the cathode leads 261 and 262 in either of the groups of the segment leads 22 and the groups of the grid leads 24.

Referring further to FIG. 3, it is to be noted that the grid supports 23 are formed on the back surface of the substrate 20 and yet are accessible from the front side of the substrate 20 through a notch formed for each of the grid supports 23 between protrusions 28 extended sideways from the body of the substrate 20 beyond the grid supports 23. It will be understood that the free ends of the protrusions 28 define the width of the whole base plate assembly 12 and serve to protect the electroconductive film formed on the inside surface of the vacuum envelope 1] against damage. The grid supports 23 are attached to the back surfaces of the protrusions 28. The superfluous luminescent layers, if formed on the grid supports 23, do not result in spurious luminescence when viewed from the front side.

Referring finally to FIG. 4, similar components of a base plate assembly 12 according to a second embodiment of this invention are designated with like reference numerals. The provision of the protrusions 28 makes it possible to unite the grid supports 23 arranged along each side edges of the substrate 20 by a frame member (not shown) similar to the frame members 271 through 274 into a grid support frame during manufacture of the base plate assembly 20. This remarkably raises the efficiency of manufacture of the base plate assembly 20 and consequently the luminescence display tubes. The grid supports 23 may be attached to the body of the substrate 20 inside the bottom line of the notches formed between the adjacent protrusions 28 rather than to the protrusions 28. It is therefore possible to dispense with some of the protrusions 28 depicted in FIG. 4. With the protrusions 28 extended beyond protrusions 39 left after the grid supports 23 are cut from. the grid support frames attached to the substrate on the respective sides of the luminescent segments 21, it is possible to protect the electroconductive film formed on the inside surface of the vacuum envelope 11 against damages.

With the grid supports 23 attached to the front surface of the substrate 20 as in the second embodiment, it is possible to extend the grid leads 24 from the front longitudinal end surface of the substrate 20 and the segment leads 22 from the back longitudinal end sur-.

face of the substrate 20. When the grid supports 23 are attached to the back surface of the substrate 20 as in the first embodiment, it is possible to remove without any damages to the luminescent segments 21 the superfluous luminescent layers formed on the grid supports 23 by way of brushing or air-blowing with the segments 21 protected by masking.

What is claimed is:

l. A base plate assembly, including an insulative substrate, of a luminescence display tube comprising a cathode disposed in front of said substrate and means for controlling distribution of electrons emitted by said cathode on the front surface of said substrate, said assembly further including supports arranged thereon for said electron distribution controlling means along both side edges of said substrate, wherein the improvement comprises protrusions extended sideways from the body of said substrate beyond said supports for said electron distribution controlling means.

2. A base plate assembly as claimed in claim 1, each of said supports for said electron distribution controlling means having a protrusion left after cutting of said supports from at least two grid support frames, wherein said protrusions of said substrate extend beyond said protrusions of said supports.

3. A base plate assembly as claimed in claim 1, further including luminescent segments arranged on the front surface of said substrate, wherein leads for said luminescent segments are extended longitudinally outwardly of the front longitudinal end surface of said substrate and leads for said electron distribution controlling means are extended longitudinally outwardly of the back longitudinal end surface of said substrate.

4. A base plate assembly as claimed in claim 1, wherein said supports for said electron distribution controlling means are attached to the back surface of said substrate. 

1. A base plate assembly, including an insulative substrate, of a luminescence display tube comprising a cathode disposed in front of said substrate and means for controlling distribution of electrons emitted by said cathode on the front surface of said substrate, said assembly further including supports arranged thereon for sAid electron distribution controlling means along both side edges of said substrate, wherein the improvement comprises protrusions extended sideways from the body of said substrate beyond said supports for said electron distribution controlling means.
 2. A base plate assembly as claimed in claim 1, each of said supports for said electron distribution controlling means having a protrusion left after cutting of said supports from at least two grid support frames, wherein said protrusions of said substrate extend beyond said protrusions of said supports.
 3. A base plate assembly as claimed in claim 1, further including luminescent segments arranged on the front surface of said substrate, wherein leads for said luminescent segments are extended longitudinally outwardly of the front longitudinal end surface of said substrate and leads for said electron distribution controlling means are extended longitudinally outwardly of the back longitudinal end surface of said substrate.
 4. A base plate assembly as claimed in claim 1, wherein said supports for said electron distribution controlling means are attached to the back surface of said substrate. 